This proposal to study the antimicrobial molecules of porcine and chicken neutrophils is based on work being conducted at the Institute of Experimental Medicine (IEM) in St. Petersburg, Russia and is supported by preliminary collaborative studies that have been performed at UCLA. The IEM investigators have identified and partially purified potent antimicrobial peptides from the leukocytes of chickens and pigs. Preliminary studies of the chicken peptides have confirmed their antimicrobial activity, and provided composition and partial sequence data for two of the peptides.Although the peptides were cysteine-rich, they lacked the classical cysteine motif of defensins, more closely resembling "TAP" (tracheal antimicrobial peptide), a recently described endogenous peptide antibiotic of the bovine respiratory tract. This FIRCA proposal has three specific aims: 1) to purify the defensin- sized antimicrobial peptides of chicken leukocytes, ascertain their primary structures, test their ability to kill selected bacteria and fungi and compare their structures and activities with previously characterized antimicrobial peptides of other species; 2) to purify the defensin-sized antimicrobial peptides of porcine leukocytes, determine their primary structures, test their ability to kill selected bacteria and fungi and compare them with other previously characterized antimicrobial peptides; 3) to clone the avian antimicrobial proteins from genomic and cDNA libraries and determine their genetic relatedness to defensins and other antimicrobial peptides of leukocytes. This proposal extends the parent grant's scope to encompass species that would not otherwise be tested. The past decade has seen a great expansion of information about endogenous antimicrobial peptides, such as magainins, cecropins and defensins, that could play a central role in innate resistance to infection. Comparative biochemical studies of various animal species have contributed to the identification of homologous peptides in man.For example, the delineation of human defensins was made possible by earlier studies with rabbit neutrophils and macrophages, and antimicrobial granulins were first recognized in equine neutrophils. Thus, the proposed FIRCA study should not only illuminate the evolution of defensin-like peptide antibiotics, it may also provide probes to facilitate the search for novel homologs of these peptides in humans.